Shotshells are widely used in shotguns for hunting, law enforcement and military combat. Since approximately the turn of the century the dimensions of shotshells have been standardized to match one or the other of a small number of standard barrel sizes. The internal barrel diameters of shotguns are usually stated in terms of "gauges", as for example, 10, 12, 16, 20 and 28 gauges. The smaller the gauge number, the larger the internal barrel diameter and the larger the shotshell diameter. The most popular gauges today are 12 and 20 gauges.
FIG. 1A shows a simplified, partial cross-sectional and cut-away view and FIG. 1B shows an end view of typical prior art shotshell 10. Shotshell 10 comprises metal base 12 having short metal sidewall 14 to which is attached paper or plastic tube or sleeve 16 which makes up most of length 13, 15 of shotshell 10. Length 13 is the length of the shotshell before sleeve 16 is crimped (i.e. rolled or folded inward to retain the powder and shot) or after the crimp unfolds on firing. Length 15 is the length of the crimped shotshell.
Base 12, sidewall 14 and sleeve 16 hold firing cap or primer 17, base wad 18, powder 19, compression wadding 20 and shot 22 in that order. Generally, the larger powder charge 19, the higher metal sidewall 14 in order to provide extra lateral (radial) strength to shotshell 10 in the immediate vicinity of the powder explosion. End 23' of sleeve 16 is inwardly folded to provide crimped end 23 to retain shot 22 in sleeve 16. Sometimes with smaller size shot or when a rolled crimp is used, a thin wad (not shown) is provided between shot 22 and crimped end 23 of sleeve 16 to insure that shot 22 is firmly retained within sleeve 16.
FIG. 2 shows a simplified, partial cross-sectional and cut-away view of prior art shotgun potion 11 with prior art shotshell 10 in place ready for firing. Shotgun portion 11 has chamber 27 for receiving shotshell 10. Inner diameter 24 of shotshell 10 is about equal to inner diameter 28 of shotgun barrel 30. Cone shaped transition zone 29 is provided between chamber 27 and barrel 30. This is referred to in the art as a "forcing cone". Chamber 27 is closed by breech 31 containing a firing pin indicated by arrow 33 aligned with primer cap 17.
Inner diameter 34 of chamber 27 matches outer diameter 36 of shotshell 10 with enough clearance so that shotshell 10 may be easily inserted and removed. Chamber 27 and breech 31 provide structural support for the relative weak casing of shotshell 10 so as resist the radial outward force created when powder 19 burns. When shotshell 10 is fired, compression wadding 20 seals against inside wall 38 of shotgun barrel 30 to propel shot 22. In this way, the full force of the rapidly expanding gases from burning powder 19 is transferred to shot 22 and little if any gas escapes around or through shot 22.
Most shotshells today come in one of two standard lengths, that is, 2.75 inches ("standard") and 3.0 inches ("magnum") and shotguns are chambered to accept either the 2.75 inch standard shells or both the 2.75 inch standard and the 3.0 inch magnum shells. A shotgun chambered for magnums will general safely fire either standard or magnum shotshells but a shotgun chambered for standard shotshells will not safely fire the longer magnum shells.
The designated "length" of shotshell 10 (e.g., 2.75 inch standard or 3.0 inch magnum) refers to length 35 of chamber 27 needed to accommodate shotshell 10 when fired, and corresponds about to overall shotshell length 13 before end 23' of sleeve 16 is crimped. Chamber length 35 must be large enough to allow crimped end 23' of sleeve 16 to completely open out against inner wall 39 of chamber 27 and provide a clear path for shot 22 and wad 20 to pass out of sleeve 16 and into barrel 30. If sleeve end 23 cannot fully open, then a constriction is created partially blocking barrel entrance 29. This can lead to excessive pressure and possible rupture of the chamber or breech.
A standard 2.75 inch shotshell has uncrimped length 13 of about 2.75 inches and crimped length 15 of typically about 2.375-2.5 inches. When shotshell 10 is fired, crimped end 23 unfolds against wall 39 of chamber 27, restoring the shell to approximately uncrimped length 13. Length 35 of chamber 27 is sufficient to accommodate uncrimped shotshell length 13 between breech 31 and forcing cone entrance 29 to barrel 30, leaving at most very small gap 25 therebetween. The close proximity of unfolded shell end 23' and forcing cone 29 allows shot 22 and wadding 20 to pass smoothly from sleeve 16 into barrel 30 so that the wadding can make a substantially gas-tight seal against interior wall 38 of barrel 30.
The 2.75 inch "standard" length for shotshells dates back to the days when such shells used black powder. Because black powder was a comparatively weak explosive, a substantial volume of black powder was necessary to propel the shot from the shotgun with sufficient force to be effective. Thus, a relatively long shell casing was required to accommodate the volume of black powder needed. The 2.75 inch shotshell length was adopted by many gun manufacturers of that era because it was able to hold the desired amount of black powder and they chambered their shotguns accordingly. This became the de-facto standard that persisted long after the use of black powder was discontinued, and still remains the standard today. While most new guns are chambered for both 2.75 inch standard and 3.0 inch magnum shotshells, the 2.75 inch standard shotshell is still the predominant shell type because of the very large number of existing guns chambered for that shell length which cannot safely use the 3.0 inch magnum shell.
Once black powder was replaced by modern smokeless power in the early 1900's, the large volume of space in the 2.75 inch standard shell length was no longer needed for the powder charge because the smokeless powder was much more powerful. The empty space could not be filled with smokeless powder because that would create a grave risk of gun rupture, especially with older guns designed for use with black powder. Whether or not any attempt was ever made to shorten the shell casings without modifying the gun chamber is lost in the history of gun and ammunition development near the beginning of the present century. If such attempts were made they were apparently unsuccessful and the standard 2.75 inch shell length was retained and the excess space in the shell filled by additional wadding or shot cups or other space-takers. Even today, almost a century after smokeless powder came into widespread use, virtually all shotguns are still manufactured to accept the 2.75 inch standard shell length in their chambers and magazines.
Many shotguns are of the manual (pump) or semiautomatic (gas or blow-back operated) repeating variety. Because shotshells are relatively large, they are usually held end-to-end in tubular magazines mounted under the barrel. Clip-type magazines where shells are held side-by-side are generally not used with shotguns because they are too bulky.
The number of shells that a tubular magazine can accommodate is limited by the free magazine length divided by the shell length. Some extra space is provided in the tubular magazines to accommodate the coiled spring that pushes the shells out of the magazine as the loading action is cycled.
Most shotgun magazines hold four 2.75 inch standard shells. An additional round may be held in the chamber, giving a typical maximum load of five shells. Extended magazines, which are common on military and police shotguns, may hold five to ten shells giving a total of six to eleven shells, but further lengthening of the tubular magazine is not desirable because it makes the shotgun unwieldy.
While five shells may be adequate for most hunting situations, in law enforcement and military combat there is a great premium on having as many shells as possible in the magazine. This is because shotguns are slow and awkward to reload in high stress, fire-fight situations. The tubular magazine must be refilled one shell at a time. Where two opposing combatants (e.g. police versus criminal or soldier versus soldier) are armed with shotguns, the one with one or more extra rounds in his weapon has a great advantage, a potentially life saving advantage.
Despite the desirability of being able to carry more shotshells in a standard shotgun magazine, little progress has been made since the first tubular magazine shotguns were introduced in the early part of the century. The shotshell and magazine length of most shotgun designs have remained virtually unchanged. If anything, newer forms of ammunition have tended to be longer (e.g., the magnum shell) which decreases the effective magazine capacity. Thus, a long unsatisfied need exists for shotshells which permit a larger magazine load and which fire safely and effectively without weapon modification.